Underwater explosive charge



Aug. 26, 1969 w; 5 ANDR-Ew 3,463,085

UNDERWATER EXPLOSIVE CHARGE Original Filed Feb. 23, 1967 2 Sheets-Sheet 1 Aug. 26, 1969 w. s. K. ANDREW 5 UNDERWATER EXPLOSIVE CHARGE Original Filed Feb. 23, 1967 2 Sheets-Sheet 2 I O l O X Jinan/20E MMQM fizmzrzzeefiwzeaw mfcfnszy w fi United States Patent 3,463,085 UNDERWATER EXPLOSIVE CHARGE William Stewart Kerr Andrew, deceased, late of West Kilbride, Scotland, by Jeanie Andrew, sole executrix, West Kilbride, Scotland, assignor to Imperial Chemical Industries Limited, London, England, a corporation of Great Britain Continuation of application Ser. No. 618,227, Feb. 23, 1967. This application Oct. 4, 1968, Ser. No. 769,469 Claims priority, application Great Britain, Mar. 18, 1966, 11,989/66 Int. Cl. F42d 3/00 US. Cl. 102-24 8 Claims ABSTRACT OF THE DISCLOSURE An explosive charge for underwater use comprises a water-destructible explosive contained in a casing having an aperture and normally closed valve means for opening the aperture at a predetermined exterior pressure so that water will enter the casing upon sinking of the latter to a predetermined depth. The valve may take the form of a flexible flap which is displaceable away from the inner end of the aperture by the hydrostatic pressure outside the casing.

This is a continuation of Ser. No. 618,227, filed Feb. 23, 1967, and now abandoned, This invention relates to an explosive charge suitable for underwater use, as for example, in marine seismographic prospecting.

In marine seismographic prospecting, charges of explosive primed with detonators are fired underwater to generate seismic pulses. The prospecting operations are often carried out under diflicult operational conditions and there is a danger of charges being accidently lost in the sea. The explosives used are usually of a waterdestructible character but they are usually in tinplate canisters which can prevent ingress of the sea water for several weeks before the casing corrodes and ruptures to allow the water to desensitise the explosive contents. There is, therefore, a danger of charges being washed up on the shore or dragged up from the sea whilst still in a live condition.

It is an object of this invention to provide an explosive charge suitable for underwater use which will become desensitised when placed underwater for a predeterminable period.

In accordance with the invention an explosive charge for underwater use comprises a water-destructible explosive composition contained in a casing having an aperture controlled by valve means which is capable of being opened by hydrostatic pressure to permit water to enter the casing.

The valve means conveniently comprises a valve member obturating said aperture and means yieldably urging the valve member into a position closing the aperture. For example, the valve member may be anchored on the casing by means of a resilient member arranged to bias the valve member to the closing position.

In one form of the invention the valve means comprises a valve member and anchoring means formed as an integral moulding from elastomeric material such as, for example, rubber or a thermoplastic material such as, for example, polyethylene or polyvinyl chloride. Preferably the moulding comprises a flat, flexible valve member formed on the end of a shank adapted to fit into a corresponding anchoring aperture in the casing.

The casing may conveniently be any of the waterresistant casings normally used for underwater explosives. Tinplate, terneplate or aluminum canisters are eminently ICE satisfactory. The explosive may also be any of the explosive powder compositions used for underwater operations. Compositions based on sensitised ammonium nitrate are normally used for seismographic prospecting operations.

Further features of the invention are included in a preferred explosive charge which is hereinafter particularly described, by way of example only, with reference to the accompanying drawings wherein:

FIG. 1 shows a longitudinal section of the casing of an explosive charge;

FIG. 2 is a fragmentary section of the casing of FIG. 1 on a larger scale;

FIGS. 3 and 4 show end views of the portion of easing shown in FIG. 2 from the interior and exterior respectively.

The explosive charge comprises explosive composition (not shown) contained within a casing 1 having a body portion 2 and ends 3 and 4. The end 3 is provided with a pocket 5 adapted to accommodate detonation initiating means (booster, detonator and the like as required) and the end 4 is provided with four apertures 6 closed by a rubber valve member 7. The valve member 7 is an integral moulding providing a cylindrical shank portion 8, plugged into an aperture 9 in the end 4, and a thin flexible annular portion 10 extending over the apertures 6.

When the explosive charge is immersed in water and the charge sinks to a depth at which the hydrostatic pressure causes the portion 10 of the valve member 7 to flex, and open the apertures 6, water enters the casing 1 and eventually the explosive charge is desensitised. The rate at which the water enters is accelerated as the charge sinks.

The depth of immersion at which the explosive charge will be desensitised may be predetermined by variation of the nature, flexibility and dimensions of the portion 10 of the valve member 7. The rate at which the water penetrates the charge may also be controlled by the above factors and also by variation of the size and number of the apertures 6.

What is claimed is:

1. An explosive charge for underwater use comprising a casing having at least one aperture therethrough, a water-destructible explosive composition in said casing and exposed to said aperture, and means associated with said aperture for permitting water to enter said aperture from the outside upon sinking of said casing to a predetermined depth independent of the length of time of immersion to thereby contact and desensitise said eX- plosive inside said casing, said means including valve means carried by said casing and exposed to ambient pressure, said valve means normally closing said aperture against ingress of water and being responsive to a predetermined pressure outside said casing corresponding to said predetermined depth to open said aperture to the water.

2. An explosive charge as claimed in claim 1 wherein the valve means comprises a valve member obturating the aperture and means yieldably urging the valve member into a position closing the aperture.

3. An explosive charge as claimed in claim 2 wherein the valve member is anchored on the casing by means of a resilient member arranged to bias the valve member to the closing position.

4. An explosive charge as claimed in claim 1 wherein the valve means comprises a valve member and anchoring means formed as an integral moulding from elastomeric material.

5. An explosive charge as claimed in claim 4 wherein the elastomeric material is selected from the group consisting of rubber, polyethylene and polyvinyl chloride.

6. An explosive charge as claimed in claim 4 wherein the moulding comprises a flat, flexible valve memb r formed on the end of a shank adapted to fit into an anchoring aperture in the casing.

7. An explosive charge as claimed in claim 1 wherein the material of the casing is selected from the group consisting of tinplate, terneplate and aluminum.

8. An explosive charge as claimed in claim 1 wherein the water-destructible explosive composition is based on sensitised ammonium nitrate.

References Cited UNITED STATES PATENTS Walsh 102-10 Martena 102-7 Grifiith et al. 102-24 Grilfith et al. 102-24 VERLIN R. PENDEGRASS, Primary Examiner 

